There are many diseases or disorders that are inflammatory in their nature. One of the major problems associated with existing treatments of inflammatory condition is inadequate efficacy and/or the prevalence of side effects. Inflammatory diseases that affect the population include asthma, inflammatory bowel disease, rheumatoid arthritis, osteoarthritis, rhinitis, conjunctivitis and dermatitis. Inflammation is also a common cause of pain.
The enzyme cyclooxygenase (COX) converts arachidonic acid to an unstable intermediate, prostaglandin H2 (PGH2) which is further converted to other prostaglandins including PGE2, PGF2α, PGD2, prostacyclin and thromboxane A2. These arachidonic acid metabolites are known to have pronounced physiological and pathophysiological activity including pro-inflammatory effects. The COX enzyme exists in two forms, one that is constitutively expressed in many cells and tissues (COX-1), and other that in most cells and tissues are induced by pro-inflammatory stimuli, such as cytokines, during an inflammatory response (COX-2).
Among all prostaglandin metabolites, PGE2 is particularly known to be a strong pro-inflammatory mediator, and is also known to induce fever and pain. Consequently, numerous drugs have been developed with a view to inhibiting the formation of PGE2, including “NSAIDs” (non-steroidal anti-inflammatory drugs) and “coxibs” (selective COX-2 inhibitors). These drugs act predominantly by inhibition of COX-1 and/or COX-2, thereby reducing the formation of PGE2. However, the inhibition of COXs has the disadvantage that it results in the reduction of the formation of all metabolites of PGH2, thereby decreasing the beneficial properties of some of the metabolites. In view of this, drugs which act by inhibition of COXs are therefore known/suspected to cause adverse biological effects. For example, the non-selective inhibition of COXs by NSAIDs may give rise to gastrointestinal side-effects and affect platelet and renal function. Even the selective inhibition of COX-2 by coxibs, whilst reducing such gastrointestinal side-effects, is believed to give rise to cardiovascular problems.
A combination of pharmacological, genetic and neutralizing antibody approaches demonstrates the importance of PGE2 in inflammation. The conversion of PGH2 to PGE2 by prostaglandin E synthases (PGES) may therefore represent a pivotal step in the propagation of inflammatory stimuli. Microsomal prostaglandin E synthase-1 (mPGES-1) is an inducible PGES after exposure to pro-inflammatory stimuli. mPGES-1 is induced in the periphery and CNS by inflammation and represents therefore a target for acute and chronic inflammatory disorders. PGE2 is a major prostanoid, produced from arachidonic acid liberated by phospholipases (PLAs), which drives the inflammatory processes. Arachidonic acid is transformed by the action of prostaglandin H synthase (PGH synthase, cycloxygenase) into PGH2 which is a substrate for mPGES-1, which is the terminal enzyme transforming PGH2 to the pro-inflammatory PGE2.
PGH2 may be transformed to PGE2 by prostaglandin E synthases (PGES). There are two microsomal prostaglandin E synthases (mPGES-1 and mPGES-2), and one cytosolic prostaglandin E synthase (cPGES). Thus, agents that are capable of inhibiting the action of mPGES-1, and thus reducing the formation of the specific arachidonic acid metabolite PGE2, are likely to be of benefit in the treatment of inflammation. Further, agents that are capable of inhibiting the action of the proteins involved in the synthesis of the leukotrienes are also likely to be of benefit in the treatment of asthma and COPD.
Blocking the formation of PGE2 in animal models of inflammatory pain results in reduced inflammation, pain and fever response (Kojima et. al, The Journal of Immunology 2008, 180, 8361-6; Xu et. al., The Journal of Pharmacology and Experimental Therapeutics 2008, 326, 754-63). In abdominal aortic aneurism, inflammation leads to connective tissue degradation and smooth muscle apoptosis ultimately leading to aortic dilation and rupture. In animals lacking mPGES-1 a slower disease progression and disease severity has been demonstrated (Wang et. al., Circulation, 2008, 117, 1302-1309).
Several lines of evidence indicate that PGE2 is involved in malignant growth. PGE2 facilitates tumor progression by stimulation of cellular proliferation and angiogenesis and by modulation of immunosupression. In support of a role for PGE2 in cancers, genetic deletion of mPGES-1 in mice suppresses the intestinal tumourogenesis (Nakanishi et. al., Cancer Research 2008, 68(9), 3251-9). In human beings, mPGES-1 is also upregulated in cancers such as colorectal cancer (Schroder Journal of Lipid Research 2006, 47, 1071-80).
Myositis is chronic muscle disorder characterized by muscle weakness and fatigue. Proinflammatory cytokines and prostanoids have been implicated in the development of myositis. In skeletal muscle tissue from patients suffering from myositis an increase in cyclooxygenases and mPGES-1 has been demonstrated, implicating mPGES-1 as a target for treating this condition. (Korotkova Annals of the Rheumatic Diseases 2008, 67, 1596-1602).
In atherosclerosis inflammation of the vasculature leads to atheroma formation that eventually may progress into infarction. In patients with carotid atherosclerosis an increase in mPGES-1 in plaque regions have been reported (Gomez-Hernandez Atherosclerosis 2006, 187, 139-49). In an animal model of atherosclerosis, mice lacking the mPGES-1 receptor were found to show a retarded atherogenesis and a concomitant reduction in macrophage-derived foam cells together with an increase in vascular smooth muscle cells (Wang, Proceedings of National Academy of Sciences 2006, 103(39), 14507-12).
PCT publication numbers WO2006/063466, WO2007/059610, WO2010/034796, and WO2010/100249 disclose numerous heterocyclic compounds which are shown to be inhibitors of microsomal prostaglandin E synthase-1 (mPGES-1) enzyme.
The present invention is directed to novel compounds that are selective inhibitors of the mPGES-1 enzyme and would therefore be useful for the treatment of pain and inflammation in a variety of diseases or conditions.